Diabetes results from insufficient functional pancreatic ?-cell mass to meet peripheral insulin demands. ?-cell failure can occur in T2D due to loss of ?-cell identity or de-differentiation, with recent studies suggesting that loss of the mitochondrial gene expression program heralds the immature ?-cell state. ?-cells rely upon mitochondrial respiration to generate the energy necessary for the metabolic demands of insulin biosynthesis, processing, and secretion. Indeed, defects in mitochondrial structure, function, and DNA levels have been reported in the ?-cells of patients with type 2 diabetes (T2D). Defects in mitochondrial structure and function are characteristic of impairments in the mitochondrial life cycle, which maintains functional mitochondrial mass via a balance of biogenesis and turnover. It is not clear, however, if impaired mitochondria are necessary and sufficient to directly induce ?-cell immaturity. Interestingly, our preliminary data suggest that genetic loss of biogenesis or mitophagy reduces ?-cell maturity and mass, which is not due to impaired ?-cell replication or survival. Therefore, our goal is to dissect the mechanistic contribution of mitochondrial biogenesis and turnover to ?-cell maturity and elucidate their contribution to diabetes pathogenesis. The central hypothesis to be tested is that defects in the mitochondrial life cycle induce a retrograde signaling cascade that impairs ?-cell identity. We will test this hypothesis by the following approach: Specific Aim 1 will elucidate the effect of metabolic overload on the mitochondrial life cycle and its control of ?-cell identity. Specific Aim 2 will determine the contribution of mitochondria derived oxidative damage to the development of ?-cell immaturity. Specific Aim 3 will delineate the role of the integrated stress response to consolidate retrograde signals inducing ?-cell immaturity following mitochondrial dysfunction. We anticipate obtaining a clear understanding of the importance and translational relevance of the mitochondrial life cycle by revealing the key effectors that mediate mito-nuclear crosstalk and impact ?-cell identity. These results should re-define the role of mitochondria in diabetes pathogenesis and could open new possibilities to re-program immature ?-cells back to a mature state to treat diabetes in Veterans.